This trial is an open-label, randomized, multicenter study of the safety and efficacy of intravenous (IV) administration of cidofovir (HPMPC) for the treatment of relapsing cytomegalovirus (CMV) retinitis in persons with AIDS. The subjects recruited into this trial will be randomized to either a low-or high-dose maintenance treatment group and probenecid and cidofovir will be given to them at no charge on a compassionate basis from Gilead, Inc. All other costs will be borne by the patient or the patient's insurance.